1. Field of the Invention
This invention relates generally to an axial flow fan having at least one auxiliary blade.
2. Description of the Prior Art
Hitherto, an axial flow fan finds a wide application because it provides a large quantity of air flow despite its small size. The axial flow fans may be classified into two types, i.e., a so-called non-pressure, open type, such as a cooling fan or blower, in which a pressure resistance is not present on a suction side or a discharge side of the fan in the close vicinity thereof, and a pressure resistance type, such as an automotive radiator fan, oil cooler fan, or an air conditioning fan, in which there is some pressure resistance either on the suction side or the discharge side of the fan, or those fans which are used in a pressurized condition, such as in a ram airflow.
In either case, an identical design principle is incorporated therein. Accordingly, a non-pressure, open type fan is often used as a pressure resistance type fan, irrespective of the pattern of air streams, thus resulting in a lowered efficiency and a high noise level.
According to the axial flow fan of prior applications of the present inventors, when applied to non-pressure open type fans, the quantity of discharge air may be increased, due to centrifugal air streams created by an auxiliary blade provided therefor, as compared with a prior art non-pressure, open type cooling fan and blower which does not produce centrifugal air streams, and, in addition, air may be blown over a large range of an area.
In addition, according to such prior applications, when applied to a pressure resistance type fan, a high quantity of air stream, as well as high operational efficiency, may be achieved with an improved noise level, due to the centrifugal air streams, as compared with a prior art fan, which does not produce centrifugal air streams, and in which a pressure resistance is present either on a suction side or on a discharge side of the fan, or on both sides of the fan.
The inventors made a continued study on this subject, and by paying attention to the fact that the trailing edge of a fan blade contributes to an increase in the quantity of discharge air and efficiency, the inventors made the present invention by improving the fans of their prior applications.